The present invention relates to a stacked electronic part having a stacked structure provided with a green body made of ceramics and an internal electrode and a method of manufacturing the stacked electronic part.
In general, a stacked electronic part formed from a thermistor, a capacitor, an inductor, LTCC (Low Temperature Co-fired Ceramics) and a varistor that has a ceramic green body, an internal electrode and an external electrode, and from a complex thereof is mounted on a wiring board, such as a printed circuit board, and the external electrode is soldered in a prescribed connection point. On that occasion, if an terminal electrode composed of an Ni layer and an Sn layer is formed, by plating, on an external electrode (a front-end electrode) made of, for example, Ag, is used, the bonding properties of a solder to the substrate are improved and productivity can be improved.
In order to prevent the worsening of the electrical properties of a stacked electronic part that is caused by the entry of a plating electrolyte into the green body of the part in the plating process for forming such a terminal electrode, for example, Japanese Patent No. 2700978 proposes an electronic part which is such that a silicone resin or a phenol resin is impregnated in all pores that are present on the surface part of a ceramic green body of the electronic part.
Incidentally, when the present inventors examined the physical properties and electrical properties of the above-described various kinds of stacked electronic parts in which a terminal electrode is formed on an external electrode by plating, it became evident that for example, in a stacked electronic part having a porous ceramic green body, such as a PTC (Positive Temperature Coefficient) thermistor, in particular, the surface and the subsurface part of the green body, and even the interior of the green body may sometimes be plated, with the result that a decrease in the insulating characteristics between external electrodes or a short circuit occurs, and that occasionally the plating reaches an internal electrode, posing the problem that the functions of the products are lost.
Specifically, when external electrodes (front-end electrodes) were formed at both ends of a PTC thermistor and the formation of Ni/Sn terminal electrodes was performed by electroplating, which was barrel plating, the plating was deposited on the whole surface of the ceramic green body. As a result of an examination of the element distribution of Ni and Sn on a section of this green body by use of an EPMA (Electron Probe Microanalyzer), it became apparent that a large amount of Ni is deposited on the subsurface part and that Ni is deposited also in a deeper part. From this, it is estimated that the plating liquid enters the interior of open pores that reach an internal electrode and that by the power supply from the internal electrode, the plating becomes deposited and grows from the interior of the green body. Such a phenomenon of plating deposition to a green body is similarly observed also when electroless plating using a catalyst is started and when electroless plating is started by the contact process without using a catalyst. Also in this case, it is estimated that plating becomes deposited and grows from the interior of open pores that reach the internal electrode. In contrast to this, when the whole surface of a ceramic green body was impregnated with a silicone resin by using a conventional method disclosed in Japanese Patent No. 2700978, it was ascertained that under some resin impregnation conditions, the deposition of a plating on the ceramic green body cannot be sufficiently suppressed.
Therefore, the present invention has been made in view of the above-described circumstances and has as its object the provision of a stacked electronic part that can sufficiently suppress plating deposition on the surface of a porous green body made of ceramics even when a terminal electrode is formed on an external electrode by plating, thereby enabling a decrease in the reliability of products to be prevented, and of a method of manufacturing the stacked electronic part.